Articulation Apparatus for External Fixation Device

ABSTRACT

An articulation element consisting of a plurality of adjustable jaw pairs for the purposes of fixating the relative position of coupled bars and for bone pins of an external bone fixator. Each of the adjustable jaws consists of a pair of hemispherical jaw elements contained within a spherical housing. A passage is eccentrically arranged through the jaw elements to accept the pin or bar. The jaw elements have interposed between them a spring element that serves to bias the jaw elements in the closed position. Pins serve to provisionally lock the jaw elements in the closed position. Spring loaded buttons act to release the pins thereby allowing the jaw elements to open accepting the pin or bar. The jaws are attached in a back to back fashion through the use of a threaded collar which acts as a turnbuckle pulling the jaws together when tightened.

This application is a continuation of U.S. patent application Ser. No.13/038,103, filed Mar. 1, 2011, (now U.S. Pat. No. 8,361,073), which isa continuation of U.S. patent application Ser. No. 12/727,533, filedMar. 19, 2010 (now U.S. Pat. No. 7,938,829), which is a continuation ofU.S. patent application Ser. No. 11/708,987, filed Feb. 21, 2007, (nowU.S. Pat. No. 7,708,736), which claims the benefit of U.S. ProvisionalApplication No. 60/775,565 filed Feb. 22, 2006, which are allincorporated herein by reference in their entirety.

FIELD OF THE INVENTION

This innovation relates to an articulation element employed in thefixation of cylindrical components, namely bone pins and bar systems,utilized in the field of external fixation.

BACKGROUND OF THE INVENTION

External fixation devices typically include external frames which areused in conjunction with bone pins which are surgically placed into thebone fragments to be repaired or immobilized to promote healing. Suchexternal fixation systems allow for particular placement of the bonepins that hold the bone fragment into which they are inserted, as thereare often characteristics in the affected area that require delicateplacement of pins such as proximity to nerves or arteries, or aroundjoints.

The field of external fixation varies widely comprising many differenttypes of apparatus. Typically bone pins are inserted through the softtissue into the bone fragments; devices are then affixed to the pins andserve to connect the various fragments in such a way as to maintaincorrect anatomic position during the healing process. As is often thecase, placement of the bone pins must be carefully selected to avoiddamaging structures such as blood vessels, nerves, tendons, etc.Additionally consideration must be given to the structural integrity ofthe bone stock in combination with geometric stability considerations ofthe final construct.

Earlier fixation systems required prior assembly (complete or partial).One such know system uses a clamping type articulation element for therelative positioning of fixation bars and bone pins of an externalfixation device. A drawback of such a device is that the articulationelements require being mounted on the fixation bars or the pins viatheir ends in advance of attachment. Until the clamping mechanism insuch device is locked, the components are not held firmly and can movewith respect to one another, making it difficult to hold all componentsin their proper relative orientation prior to or during final locking ofthe device.

Other known external fixation devices have been developed where thecomponents of the external fixation devices are assembled after the pinshave been inserted into the optimum position with respect to the bonefragment to be held and the tissue surrounding them. Typically thefixation bars making up the frame of the fixation device are then placedbetween the bone pins and articulation elements are used to connect thebars and the pins. It is often necessary that these articulationelements allow the bars or pins to be held at variable angles.

To address these concerns while providing maximum utility and ease ofuse; manufacturers have sought to develop fixation devices that allowfor the placement of the bone pins to be independent of the externalsupporting structures that ultimately connect the pins together. Incomplex fractures there is often a need to place many pins, eitherbecause there are many fragments, or due to the poor quality of the boneand/or the nature of the fracture. Many pins, many of which will presentthemselves in different attitudes and inclinations, create a challengewhen it comes time to connect them to the external structure. For thisreason it is imperative to provide as many degrees of freedom whenconstructing an articulation element.

A simple analog to this condition is the case of the simply supportedbeam having more than 2 simple supports. This condition is characterizedas being overly constrained. Unless the beam or the foundation is ofsufficient flexibility it is impossible to share the load evenly acrossall of the multiple supports. To provide a flexible beam would defeat togoal of external fixation; we therefore need to provide a support systemin the way of articulation elements that have the placement flexibilityto evenly support the external structure.

One known prior art system describes an articulation component havingtwo cylindrical joints with a revolute joint interposed between them.The characteristic mobility of this construct is two translations andthree rotations for a total of five degrees of freedom. A known suchsystem describes a similar device with the exception that the interposedrevolute joint is replaced with a spherical joint. The characteristicmobility of this construct is two translations and five rotations for atotal of 7 degrees of freedom. One could argue that more than 6 degreesof freedom is redundant and to some extent that is true but these extradegrees of freedom, redundant or not, make the placement of the devicemore flexible. This added spherical joint does however come at someexpense, namely the pin to bar centerline distance must be increased,which makes for a bulkier construct while at the same time increasingthe moment loading on the joints themselves.

The foregoing is believed to describe prior art systems as set forth,for example, in U.S. Pat. Nos. 6,080,153 and 7,048,735 (so called Jet-XUnilateral Fixation System), and EP 0321472.

SUMMARY OF THE INVENTION

The present invention provides advancements in the state of the relevantart by, inter alia, providing a an articulation element employed in thefixation of cylindrical components, namely bone pins and bar systems,utilized in the field of external fixation.

In accordance with one aspect of the present invention, the presentinvention aims to provide greater placement flexibility in a morecompact construct than is presently available. It comprises theplacement of fixation elements on either side of a fracture. Thesefixation elements are commonly referred to as pins, whereby one or morepins are screwed into a bone. One or more pins are located on eitherside of a fracture and connected to a bar via a clamp and/or a clampingsystem. The present invention relates to connecting pins with one ormore bars in order to fixate a fracture. Such bars may also be connectedto other bars or structures, if needed. In connecting pins to rods, itis advantageous to have mobility in a clamping system to allow for easeof placement and/or post placement manipulation.

One illustrative embodiment of the present invention comprises two (2)independent but connected clamp jaws, each clamp jaw being set in aclamp housing. Each clamp jaw comprises two (2) clamp jaw halves. Theclamp jaw halves are shaped such that a clamp jaw is able to open andclose around a bar or pin. In this embodiment of the present invention,the clamp jaw is able to clamp around a bar, while simultaneously, aconnected corresponding clamp jaw is able to pivot about an axis normalto the axis of a pin or bar that is being clamped. Clamp jaw halves maybe circular in shape to surround a pin or bar with a circular crosssection. The clamp jaw halves may also be shaped to correspond to thecross section of the shape of the pin or bar being clamped. In anotherembodiment of the present invention, the clamp jaws may also beconnected such that the clamp jaws also allows a bar or pin to rotateand approximately and/or equal to 20 degrees while clamped to allow forgreater range and ease of positioning.

In alternative embodiments of the present invention, a spring is used tobias each clamp jaw half into the closed and/or clamped position. Eachclamp jaw half is held in place by a jaw pin which engages acorresponding hole. In one embodiment of the present invention, thecorresponding hole may comprise a specially milled shape and/or form.The jaw pins serve to limit the amount of travel of the clamp jaw halvesand to lock the clamp jaw halves into the closed and/or clampedposition. The jaw pins are preloaded into a locked position whereby thejaw pins are engaged with the hole in the jaw halves with a disc spring.The disc spring acts like a pressure plate spring and is made up of aseries of radial levers connected around a periphery. Spring levers holdeach jaw pin in place and allow each jaw pin to come into contact with arelease button. The release button is concentric with the jaw pin andthe disc spring. Application of an axial force on the release buttonscauses retraction of the jaw pins in the opposite direction. Whenpressure is applied to the release buttons, such pressure causes the jawpins to disengage from the clamp jaw halves, allowing the clamp jawhalves to open around the bar or pin. Removal of pressure will cause thejaw pins to re-insert into the holes in the clamp housing and a bar orpin may be placed in the clamp jaws and locked into place. A bar in aclamp jaw is able to rotate and slide about an axis orthogonal to thecorresponding pin axis and pivot about the pin axis.

In the illustrative embodiment of the present invention, two (2) clamphousings are connected to each other by a collar. The collar has aninterior diameter which comprises both a right hand female thread andleft hand female thread. Each clamp housing also comprises acorresponding right male thread and a left male thread which attach theclamp housings to the collar. The clamp housings may be keyed to eachother such that the clamp housings are limited in rotation to 180degrees relative to each other. This prevents the clamp housings fromhaving an unequal thread engagement in the collar and limits unnecessaryrange of motion.

In another embodiment of the present invention, each clamp housing withcorresponding clamp jaw, also comprises two corresponding clutch plateswhich slide along an axis concentric with a collar. The clutch platesare keyed to the clamp housing in which they slide and bear against theclamp jaw halves and corresponding clutch plate. When the collar istightened, the collar forces the clutch plates against each other andforces the clamp jaw halves into a respective clamp housing. The actionlocks the clamp jaw halves to the bar or pin and the clamp housings toeach other fixating the clamping system. In other embodiments of thepresent invention, the clutch plates may be smooth and/or may beserrated.

In embodiments of the present invention for applications with low loadand/or for accommodating less weight, the clutch plates could be smooth.This may be useful for fractures of the upper extremities. In suchembodiment of the present invention directed at low load applications,the clamp jaw halves could comprise a smooth outer spherical surface. Inyet another embodiment of the present invention for applications withhigher load and/or accommodating more weight, the clutch plates could beserrated and/or comprise clamp jaw halves that may comprise a fish scaleand/or textured outer surface. In another embodiment of the presentinvention, a collar and clamp housings may comprise a tapered formand/or threaded diameters, for example, pipe thread, whereby in additionto bringing the two clamp housings together axially, the threadeddiameters would squeeze the clamp bodies radially further tightening andclamping the clamp jaw halves.

Advantages of the present invention comprise the following: the presentinvention allows for one-handed application; includes one lock perjoint; allows for greater degrees of freedom in mounting; allows forgross manipulation; accommodates multiple indications; comprises fewcomponents; and requires minimal training.

It will be appreciated by those skilled in the art that the foregoingbrief description and the following detailed description are exemplaryand explanatory of this invention, and are not intended to berestrictive thereof or limiting of the advantages which can be achievedby this invention. Thus, the accompanying drawings, referred to hereinand constituting a part hereof, illustrate preferred embodiments of thisinvention, and, together with the detailed description, serve to explainthe principles of this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional aspects, features, and advantages of the invention, both asto its structure and operation, will be understood and will become morereadily apparent when the invention is considered in the light of thefollowing description of illustrative embodiments made in conjunctionwith the accompanying drawings, wherein:

FIG. 1 is an isometric view of an articulation element according to anillustrative embodiment of the present invention.

FIG. 2 is a second isometric view of the articulation element of FIG. 1.

FIG. 3 is a representation of the articulation element of FIGS. 1 and 2shown in schematic cross section.

FIG. 4 is a close up representation of the articulation element of FIG.3.

FIG. 5 is a cut away view of the release mechanism of the articulationelement of FIGS. 1 and 2.

FIG. 6 is a view of the pin slot in one of the jaw elements of thearticulation element of FIG. 3.

FIGS. 7 a and 7 b are views of the clutch plate of the articulationelement of FIG. 3, and

FIG. 8 is a perspective view of an illustrative external fixation systemusing the articulation element of the present invention for use on along bone application.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The external fixation system of the present invention includes anarticulation element employed in the fixation of cylindrical components,namely bone pins and bar systems. Its structure and functional detailswill be discussed in detail below in the context of an illustrativeembodiment and with reference to the figures provided.

FIGS. 1 and 2 show isometric views of an articulation element 200according to an illustrative embodiment of the present invention.

The articulation element 200 consists of a pair of back-to-backspherical clamping mechanisms 200A and 200B that act to apply clampingpressure to cylindrical bars and/or pins shown conceptually as 100 and101. The clamping mechanisms themselves consist of a pair of sphericaljaw elements 90 within each of the spherical clamping mechanisms.Release buttons 80 allow the preloaded jaw elements 90 to relax toreceive or release a rod or pin 100. Each mechanism 200A and 200B freelyrotates about axis Z (i.e., in either rotational direction about the Zaxis) as shown by arrows ZA and ZB. Lock ring 60 is used to lock therelative positions of 200A and 200B as will be described in detailbelow.

As shown in FIG. 2, bars 100 and 101 are shown in place in the clampingmechanisms 200A and 200B. Spherical jaw elements 90 (together forming anadjustable jaw pair) are disposed within the clamping mechanisms 200Aand 200B such that they allow elevation of the respective bars mountedtherein. Bar 100, shown mounted within mechanism 200A, can elevatethrough an angle A.degree. about the X axis as shown in FIG. 2. (Whileelevation only about the X axis of bar 100 in mechanism 200A is shown,similar elevation of bar 101 in mechanism 200B through an angleB.degree. about a Y axis (not shown) will be understood. The Y axis isnot necessarily in any predetermined relation to the X axis, for exampleperpendicular to X.).

In further detail and with reference to FIGS. 3-7, the articulationelement 200 consists of a pair of back-to-back spherical clampingmechanisms or members that act to apply clamping pressure to cylindricalbars and/or pins shown conceptually as 100 and 101 (FIG. 4). Theclamping mechanisms themselves consist of a pair of spherical jawelements 90 that are held with in a spherical socket 11 (FIG. 4) withinthe clamp housing 10. Located eccentrically from the spherical jaw, anangular or Gothic arch type passage is machined to form the clamping orfriction surfaces 91 (FIG. 4). Teeth, not shown, could if desired alsobe used on these surfaces 91 to provide a better gripping action.

Spherical jaw elements 90 are preloaded in a clamped or closed positionby interposition of an elastic element 70 between the jaw elements 90,shown here as a coil spring 70. The coil spring 70 is seated within acylindrical pocket 92 in each of the jaw elements 90. The elasticelement 70 serves to bias the jaw elements 90 into the closed or clampedposition around bar element 101. A tang and clevis arrangement betweenthe two jaw elements, shown as a groove 93 (FIG. 4) constrains the jawelements to rotate open and closed in a plane such that the pin and/orbar, 100, 101 can be accepted once pressure is applied to face 94 ofeach jaw element 90 (FIG. 4). Pressure on face 94 acts to open the jawelements 90. Once the pin and/or bar 100, 101 is seated the elasticelement 70 forces the jaw elements 90 to rotate closed.

Pins 20 engage both the clamp housing 10 and the jaw elements 90 andserve to limit the range of mobility of the jaw elements 90 such thatthe mouth of the jaw elements 90 (formed between faces 94 of jawelements 90) does not rotate out of the opening 12 (FIG. 4) of the clamphousing 10 by fitting into the milled recess 95 (FIGS. 4 and 7). Fullyengaged, these pins 20 keep the jaw elements 90 in the closed positionwhile still allowing for the rotation of the jaw elements 90 about theaxis of the pins 20 by fitting into the cylindrical recess 96 (FIGS. 4and 6).

With reference to FIGS. 3, 4 and 5, a single point parallel releasemechanism allows pins 20 are retracted and engaged by means of a button80 and disk spring mechanism 30. The button 80 is guided withincylindrical bore 13 in the clamp housing 10. A cylindrical bore 81within the button 80 accepts and guides the pin 20. A disk spring 30fashioned in such a way as to have a radial array of levers the outerdiameter 32 of which is fitted within a circumferential groove 83 withinthe button 80. The inner diameter 33 of the disk spring 30 engages thepin 20 in circumferential grove 21. Application of force to the button80 acts on the outer diameter 32 of the disk spring 30 which acts as alever pivoting about fulcrum 31 which bears on the clamp housing. Thisaction applies a force opposite in direction to that which was appliedto the button to circumferential grove 21 of the pin 20 causing the pin20 to retract allowing the jaw elements 90 to open in order to acceptthe pin and/or bar 100, 101. Releasing the force on the buttons 80allows the pins to re-engage the cylindrical bore 96 of the jaw elements90 keeping them in the closed position.

Once a pin and/or bar 100, 101 is engaged with both sets of jaw elements90 the pins and/or bars 100, 101 are still free to slide and rotaterelative to the jaw passage 91 while the jaw/pin/bar 90, 100, 101assemblage is allowed to pivot about the pin 20 axis. Additionallyeither half of the articulation element 200 is allowed to rotate up to180 degrees about the axis of lock ring 60.

To fixate the articulation element 200 lock ring 60 is tightened; havingboth a left hand and right hand female thread 61 on the ID it engagesthe corresponding threads on the clamp housing 10 drawing the two halvesof the articulation assembly 200 together. As the two halves cometogether pressure is applied to the clutch plates 40 which bind clutchrings 50 into the corresponding clutch plate 40 on the other side. (Seealso FIGS. 6A and 6B) The pressure effectively keeps one clutch plate 40from rotating relative to the other and the flat sides 42 key into theclamp housing 10. The spherical side 43 of 40 also applies pressure tothe spherical surface of the jaw elements 97 (FIG. 7) wedging the jawelements 90 in the clamp housing 10 which applies clamping pressure tothe pins and/or bars 100, 101.

FIG. 8 shows an illustrative embodiment of the present invention wherethe articulation elements described herein are used in an externalfixation system for a long bone application. Several rods 100 and pins101 are shown being connected via articulations elements 200 of thepresent invention and fixation ring 300. Any number of pins or rods incombination with articulation elements 200 and ring 300 may be used aswill be understood by one skilled in the art.

The present invention has been illustrated and described with respect tospecific embodiments thereof, which embodiments are merely illustrativeof the principles of the invention and are not intended to be exclusiveor otherwise limiting embodiments. For instance, although thedescription provided hereinabove along with the accompanying drawingsillustrate particular embodiments incorporating one or a few features ofthe present invention, those skilled in the art will understand in viewof the hereinabove disclosure that alternative configurations can bedevised and implemented, as well as other designs capable of achievingthe purpose and benefits of the discussed aspects of the invention.

Accordingly, although the above description of illustrative embodimentsof the present invention, as well as various illustrative modificationsand features thereof, provides many specificities, these enablingdetails should not be construed as limiting the scope of the invention,and it will be readily understood by those persons skilled in the artthat the present invention is susceptible to many modifications,adaptations, variations, omissions, additions, and equivalentimplementations without departing from this scope and withoutdiminishing its attendant advantages. It is further noted that the termsand expressions have been used as terms of description and not terms oflimitation. There is no intention to use the terms or expressions toexclude any equivalents of features shown and described or portionsthereof. It is therefore intended that the present invention is notlimited to the disclosed embodiments but should be defined in accordancewith the claims that follow.

1-20. (canceled)
 21. An articulation element for an external fixationapparatus for treating a patient, the element having a longitudinalaxis, the articulation element comprising: a first adjustable jaw pairdisposed at a first location along the longitudinal axis and configuredto capture a first rigid element of the external fixation apparatus; areference component; and a coupling mechanism coupling the firstadjustable jaw pair to the reference component, the coupling mechanismbeing disposed at a second location along the longitudinal axis andarranged so that the first adjustable jaw pair is rotatable about thelongitudinal axis relative to the reference component, the couplingmechanism comprising a curved surface interfacing with at least one jawof the first jaw pair, the first adjustable jaw pair being pivotablerelative to the reference component about a constrained first transversepivot axis that is angled relative to a first rigid element captured bythe first adjustable jaw pair.
 22. The articulation element of claim 21,wherein the reference component is a second adjustable jaw pairconfigured to apply clamping pressure to capture a second rigid elementof the external fixation apparatus, the second adjustable jaw pair beingdisposed along the longitudinal axis, the coupling mechanism beingdisposed between the first and second adjustable jaw pairs.
 23. Thearticulation element of claim 22, wherein the coupling mechanismcomprises a first component and a second component independent of anddisposed between the first and second adjustable jaw pairs, the firstand second components being pivotable relative to each other about thelongitudinal axis, the first and second adjustable jaw pairs beingpivotable relative to the respective first and second components. 24.The articulation element of claim 23, wherein the first component andsecond component each have a facing surface disposed to face each otherand cooperatively restrict rotational movement of the first componentrelative to the second component when the articulation element isclamped.
 25. The articulation element of claim 21, comprising a lockingmechanism structurally configured to lock the relative orientation ofsaid first adjustable jaw pair to said reference component.
 26. Thearticulation element of claim 21, wherein the first transverse pivotaxis intersects the longitudinal axis.
 27. The articulation element ofclaim 21, wherein the curved surface is a concave surface.
 28. Thearticulation element of claim 27, wherein the concave surface is aspherical surface.
 29. The articulation element of claim 21, wherein thecurved surface is structurally configured to engage against said atleast one jaw of the first adjustable jaw pair and selectively limitmovement of the first adjustable jaw pair about the first transverseaxis.
 30. The articulation element of claim 21, further comprising afirst biasing member disposed to apply a biasing force that acts on thefirst adjustable jaw pair to bias jaws of the first adjustable jaw pairto a closed position.
 31. The articulation element of claim 21, whereinthe first rigid element of the external fixation apparatus is one of anexternal fixation bar and a bone pin.
 32. An articulation element for anexternal fixation apparatus for treating a patient, the element having alongitudinal axis, the articulation element comprising: a first clampmechanism comprising a first adjustable jaw pair and a first engagingportion engageable with the first adjustable jaw pair to selectivelyrestrict movement of the first adjustable jaw pair, the first adjustablejaw pair being disposed at a first location along the longitudinal axisand configured to capture a first rigid element of the external fixationapparatus; and a second clamp mechanism rotatable about the longitudinalaxis relative to the first clamp mechanism, the second clamp mechanismcomprising a second adjustable jaw pair and a second engaging portionengageable with the second adjustable jaw pair to selectively restrictmovement of the second adjustable jaw pair; the first adjustable jawpair being pivotable relative to the second clamp mechanism about aconstrained first transverse pivot axis that is angled relative to afirst rigid element captured by the first adjustable jaw pair.
 33. Thearticulation element of claim 32, wherein the second adjustable jaw pairis disposed at a second location along the longitudinal axis andconfigured to capture a second rigid element of the external fixationapparatus, the first engaging portion and the second engaging portionbeing disposed between the first and second adjustable jaw pairs, thesecond adjustable jaw pair being disposed so as to pivot about a secondtransverse pivot axis.
 34. The articulation element of claim 32,comprising a locking mechanism structurally configured to lock therelative orientation of said first adjustable jaw pair to said secondadjustable jaw pair.
 35. The articulation element of claim 32, whereinthe first transverse pivot axis intersects the longitudinal axis. 36.The articulation element of claim 32, wherein the first engaging portioncomprises a first facing surface and an opposing first curved surface,and wherein the second engaging portion comprises a second facingsurface and an opposed second curved surface, the first facing surfacedisposed to face the second facing surface and cooperatively restrictrotational movement of the first engaging portion relative to the secondengaging portion when the articulation element is clamped.
 37. Thearticulation element of claim 36, wherein the first and second facingsurfaces are flat surfaces.
 38. The articulation element of claim 32,wherein the first curved surface comprises a concave surface.
 39. Thearticulation element of claim 38, wherein the concave surface is aspherical surface.
 40. The articulation element of claim 38, wherein thecurved surface is structurally configured to engage against said atleast one jaw of the first adjustable jaw pair and selectively limitmovement of the first adjustable jaw pair about the first transverseaxis.
 41. An articulation element for an external fixation apparatus fortreating a patient, the element having a longitudinal axis, thearticulation element comprising: a first adjustable jaw pair configuredto capture a first rigid element of the external fixation apparatus; asecond adjustable jaw pair configured to capture a second rigid elementof the external fixation apparatus; and a coupling mechanism disposedbetween the first and second jaw pairs so as to allow the first jaw pairto rotate relative to the second jaw pair about the longitudinal axis,the coupling mechanism being disposed at a first location on thelongitudinal axis, the coupling mechanism having a curved interfacesurface engaging at least one jaw of the first adjustable jaw pair, thefirst adjustable jaw pair being disposed so as to pivot about a firstconstrained transverse axis relative to the second adjustable jaw pairin a manner that allows movement of a first rigid element through anangle range A parallel to a plane containing the longitudinal axis whilethe first rigid element is captive in said first adjustable jaw pair.42. The articulation element of claim 41, wherein the coupling mechanismcomprises: a first rotational component adjacent the first adjustablejaw pair having a substantially flat surface and having the curvedinterface surface, the curved interface surface facing the firstadjustable jaw pair; and a second rotational component adjacent thesecond adjustable jaw pair having a substantially flat surface and asecond curved interface surface, the second curved interface surfacefacing the second adjustable jaw pair, wherein the substantially flatsurface of the first rotational component faces the substantially flatsurface of the second rotational component, and the second adjustablejaw pair being disposed so as to pivot about a second constrainedtransverse axis relative to the second adjustable jaw pair in a mannerthat allows movement of a second rigid element through an angle range Bparallel to a plane containing the longitudinal axis while the secondrigid element is captive in said second adjustable jaw pair.
 43. Thearticulation element of claim 42, wherein the first curved interfacesurface is a concave surface.
 44. The articulation element of claim 42,wherein the concave surface is a spherical surface.
 45. The articulationelement of claim 41, wherein the first transverse pivot axis isdisplaced from the first location in a first direction along thelongitudinal axis.